This is the scenario (high level).
To start with, I am the only tester (as such) in my team.
The high level design of the system:
Front-End is 'PrinMor'(developed using progress) which sends requests to "MindBox"(MB) which consists of pricing, rate sheet, rule Engines(all in one). These requests go to MB in the form of XML files. Once the request is submitted to MB, it does underwrites and checks for the rules for the particular type of request and generates the response and sends it back to the PrinMor in the form of XML file. This is the present system and it is in production.
Now we want to develop some strategies(approach) for regression testing. ie, business users want to make changes on requests and see how MB responds. They are doing testing from PrinMor to MB manually. The PrinMor application is replaced by a GUI application which consists of edit fields for each element in the request file(say kind of web-form) which will be my front-end for QTP. This GUI imports xml files and displays it in the web-form with editable fields,submits it to MB and displays the xml response in a page(xml file)
Now, with all your previous testing experience and expertness on QTP, how will you make your baseline scripts? Please give me your expert advices.

Note: This is the solution I proposed to my lead.
Parameterize fields for various combinations of input data (Iterations). I am not sure how it works.
Sorry to take your valuable time and hope I get some responses here.